1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a pouch type secondary battery.
2. Description of the Related Art
With the proliferation of portable electronic devices, such as video cameras, cellular phones, portable computers, etc., secondary batteries have been used as their driving power supplies. Especially, lithium secondary batteries can be rechargeable rapidly and has higher energy density per unit weight than conventional lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries. Accordingly, lithium secondary batteries are being actively used.
A lithium secondary battery uses lithium group oxides as cathode active materials, and a carbon material as an anode active material. An electrode assembly is fabricated by laminating a cathode plate where a cathode tap is connected to a cathode collector formed of the cathode active material, an anode plate where an anode tap is connected to an anode collector formed of the anode active material, and a separator interposed between the cathode plate and the anode plate, are laminated and wound together. The electrode assembly is contained within a metal can of an angle type or a cylinder type or in a pouch.
A lithium secondary battery can be divided into a lithium ion battery using a liquid electrolyte, and a lithium ion polymer battery using a polymer solid electrolyte, depending on the kind of electrolyte. A lithium ion polymer battery can be divided into a solid type lithium ion polymer battery containing no electrolyte, and a gel type lithium ion polymer battery using a gel type polymer electrolyte.
A lithium secondary battery using the liquid electrolyte is usually contained within a metal can of a cylinder or an angle type which is sealed by welding.
Since a can type secondary battery using a metal can has a fixed shape, the design of electronic products is limited, and reducing a volume of electronic products is difficult. Accordingly, the pouch type secondary battery has been developed by putting two electrodes, a separator and an electrolyte in a pouch made of a film and sealing the pouch.
The pouch conventionally used for the lithium ion polymer battery includes a multilayer structure laminated by a polyolefin group resin layer that is an inner heat adherent layer having a heat adhesion property as a sealing material, an intermediate aluminum layer (AL) functioning as a base material to maintain mechanical strength and a barrier layer with respect to moisture and oxygen, and an outer nylon layer functioning as a base material and a protection layer.
In a method of fabrication of a pouch type secondary battery, the pouch is first divided into a lower part receiving the electrode assembly in a receiving part of the pouch, and an upper part covering an opening of the lower part. The cathode tap is coupled to the cathode plate so as to protrude outside of the pouch. The anode tap is also coupled to the cathode plate so as to protrude outside of the pouch. An insulating tape is wrapped on a region where the cathode tap is in contact with the pouch, so as to insulate the pouch and the cathode tap. The insulating tape is also wrapped on a region where the anode tap is in contact with the pouch, so as to insulate the pouch and the anode tap. The cathode tap and the anode tap are coupled to a protection circuit substrate by bending an end portion of both the cathode tap and the anode tap.
There is a problem in that the cathode tap and the anode tap are not bent to a desirable angle because a restoration phenomenon after bending the cathode tap and the anode tap is produced by an elastic force of the insulating tape occurring in bending the end portion of both the cathode tap and the anode tap. In addition, there is a problem in that an assembly error occurs when the protection circuit substrate is coupled because the bent region is not uniform when the cathode tap and the anode tap are bent.